1. Field of the Invention
This invention relates to an electrode used for a non-aqueous electrode secondary battery, in which the dot pattern of metallic material able to be alloyed with Li on a current collector, and the non-aqueous electrolyte secondary battery using said electrode for the negative electrode.
2. Description of the Related Art
Negative electrodes for a non-aqueous electrolyte secondary battery described in JP 2001-68094-A and JP 2001-256968-A have a thin film comprising metallic materials alloyed with Li formed on a current collector of a material which is not alloyed with Li.
According to JP 2001-68094-A, a Sn thin film is formed on a current collector by an electric plating method.
According to JP 2001-256968-A, a thin film comprising a material containing Sn, Zn, Sb or the alloy as major components is formed on copper foil by an electric plating method.
Moreover, according to JP 2002-83594-A, it is described that an electrode having an active material thin film which is formed in a pattern of separated pillars made by breaks formed in the direction of thickness on a current collector and volume expansion of the active film is reduced around the breaks when the active material is intercalated by Li ions.
When the electrodes are prepared by the electric plating method, the resulting thin film can be formed by direct electrodeposition of objective metal or alloy on the current collector. Consequently, the electrodes which are excellent in the adhesion of an active material and a current collector can be obtained, compared with electrodes made by the coating method.
Also, it is more advantageous to get a cheaper manufacture cost, compared with the coating method. However, since the obtained metal-plating layer becomes very precise, an electrode tends to be influenced by volume expansion of the active material due to intercalation of Li ions, and consequently there is a fault such as a notable generation of expansion and crack in the electrode.
In the latter case, there are the following problems.
At the current collector side of the active material thin film, pillar-shaped objects are close to each other and there are not any crevices which serve as a stress relaxation place at the time of expansion of an active material.
In addition, since the diameter of each pillar-shaped object and width of the gap cannot necessarily be controlled freely, at an time of electrical charge and discharge and a cycle time, it is difficult to make the volume expansion in the active layer reduced, resulting in no sufficient utilization of the active material and no good maintenance of the active material characteristics. Therefore, it is difficult to provide an electrode which fully satisfies a load characteristic and a cycle characteristic even in the electric discharge with large electric current. Therefore, the technical establishment for controlling volume change of the active material is desired more regularly and precisely.
Accordingly, it is a first object of this invention to provide an electrode with an ability to reduce a volume expansion at the time of the electric charge and discharge and the cycle, and also to avoid the active material separation from the current collector due to the electric charge and discharge.
Further, it is another object of this invention to provide an electrode which can contribute to the improvement in characteristics of the electric charge and discharge efficiency of a battery and the rate of cycle capacity maintenance.
Also it is a further object to provide an electrode which can be charged and discharged with a large electric current and to provide a non-aqueous electrolyte secondary battery using said electrode for a negative electrode.